The present invention relates to a method for producing a filter for purifying exhaust gases and the like which are discharged from an internal combustion engine of an automobile or the like.
Conventionally, a ceramic honeycomb structure carrying oxidizing catalyst has been employed as one example of the filter. When the ceramic honeycomb structure carrying oxidizing catalyst is disposed within the exhaust gas system of the automobile, open passages of the honeycomb structure extend in the same direction as the flowing direction of the exhaust gas. Therefore, the exhaust gas flows through the open passages of the honeycomb structure in a straight line without striking against the walls of the open passages. As a result, fine particles contained within the exhaust gas are not sufficiently contacted with the oxidizing catalyst so that the exhaust gas purifying efficiency becomes poor.
Also a porous ceramic body has been used as the filter for purifying the exhaust gas. Since the open passages of this filter extend in various directions and the contact area with the exhaust gas is large, the purifying efficiency is good. But mechanical strength against vibrations or the like is remarkably inferior to that of the filter composed of the ceramic honeycomb structure.
Accordingly, one object of the present invention is to provide a filter made of porous ceramic, having improved mechanical strength and exhaust gas purifying efficiency, which is used for purifying exhaust gases discharged from an internal combustion engine of a vehicle or the like.
Another object of the present invention is to provide a method for producing a filter composed of a porous ceramic body for purifying exhaust gases, which is partially provided with a portion having higher apparent density so as to improve mechanical strength thereof.
Still another object of the present invention is to provide a method for producing a filter composed of a porous ceramic body, which is partially provided with a portion having higher apparent density so as to improve exhaust gas purifying efficiency.